Tyco International Inc.'s stock plunged nearly 23 percent today after the company's chairman said the Securities and Exchange Commission is conducting an informal inquiry into its accounting practices.

The electronics, security and telecommunications systems conglomerate lost nearly $14 billion in market value in heavy trading of 115 million shares, one of the highest one-day volume totals in U.S. history. Its stock closed at $28, down $8.25.

"In light of the recent market activity in our stock, which is not justified by any development at the company, we welcome the opportunity to respond to this request," said Dennis Kozlowski, Tyco's chairman. "We remain confident of our accounting methodology, our public disclosures and the continuing strength of our business."

The company disclosed the "non-public, informal inquiry" voluntarily and said it was cooperating with the SEC's requests for documents going back six years regarding its many acquisitions.

Tyco has been on a buying spree for a number of years, acquiring companies such as ADT Security Services Inc., a security system firm, and Praegitzer Industries Inc., a maker of printed circuit boards, for which it paid about $70 million. The Praegitzer deal just closed on Monday.

The company's stock price has suffered since October--when it was trading around $53 a share--after Texas fund manager David W. Tice questioned the way the company accounts for the many companies it buys. Tice publishes the newsletter Behind the Numbers, recommending which stocks to sell to a coterie of money managers who pay $10,000 a year for its findings.

"It is too bad that shareholders and employees lost significant amounts of money today," said Tice, who also runs the Prudent Bear Fund, a mutual fund that bets on which stocks will fall. "But the stock would never have reached this inflated level if it didn't have so many cheerleaders on Wall Street."

Tice said his mutual fund would never short-sell the stock and that he did not tip anyone off in advance of his newsletter's findings. But he did say the Securities and Exchange Commission has been in contact with him.

"It's a private inquiry," Tice said. "We have nothing to hide." He said he stands behind his original report on Tyco, which some Wall Street analysts have said had some mistakes in it.

Many Wall Street analysts continued to cheer for Tyco.

"I think the stock market totally overreacted," said John Inch, a Bear Stearns Cos. analyst who follows Tyco and has recommended that clients buy the stock. "Tyco's grown at 11 to 12 percent in the near term even without acquisitions," he said. "It should be double its price."

The silver lining, said Inch, is that when the cloud created by the the SEC investigation is removed, the company's stock will soar.

David Novosel, a fixed-income analyst for Bank One Corp., agreed. "Tyco is aggressive in accounting for mergers" when it uses stock, he said. "But there is some latitude there. Based on my knowledge of management, I'm not bothered that they've gone too far."

"We are an acquisitive company," said Tyco spokesman Brad McGee. "Because of our equity raising and debt-raising efforts, we're often reviewed by the SEC. . . . They have requested no accounting changes or amendments."

In a letter to Tyco employees, Kozlowski sought to reassure workers, saying that the company will have record-breaking earnings in 1999.

"However, we still continue to combat the effect of the unfounded accusations raised a few months ago about our accounting practices," he wrote. "We are not the first major organization to face something like this and we will certainly not be the last. Tyco will emerge from this episode even stronger than before."

CAPTION: Tyco Chairman Dennis Kozlowski defended firm's accounting.